1. Field of the Invention
The present invention relates to a process for recovering heat from a tar-containing high-temperature gas. More particularly, the invention relates to a process for recovering the heat from a tar-containing high-temperature gas generated by treating at high temperatures a fossil fuel such as crude gas generated in a coke oven, a gas generated by the thermal decomposition of coal and a gas generated by the combustion under reduced pressure of a residual oil.
2. State of the Art
Heretofore, a crude gas generated in a coke oven has been cooled by flashing ammonia water thereinto and thereafter the cooled gas is transferred by a gas refining step, whereby the sensible heat of said gas is not utilized.
In view of the above, attempts have been made to introduce a crude oil generated in a coke oven to a shell and a tube heat exchanger in an effort to recover its sensible heat. However, such crude oil generated in a coke oven contains low boiling point substances such as benzoles, high boiling point substances like tar and soluble substances like naphthalene. Therefore, at temperatures more than 450.degree. C., carbon is produced by the high temperature decomposition of tar-precipitates on the surface of the heat transfer tube in the heat exchanger, while at temperatures of 450.degree. C. and below, the high boiling point substances, like tar, condense on the surface of the heat transfer tube. At temperatures not more than 100.degree. C., the soluble substances like naphthalene condense on the heat transfer tube. As a result, these carbon and condensates thus-produced block the gas passageways in the shell and tube heat exchanger, causing the so-called coking phenomenon, thereby making it difficult to operate the heat-recovering equipment under stable conditions for a long period of time due to the clogging of the equipment and the decreased gas flow and the overall lowered heat exchange efficiency.
Attempts have also been made to spray the crude gas generated in a coke oven with a high boiling point oil such as tar distilled from a crude gas generated in a coke oven in an effort to bring the tar and crude gas into direct contact with each other to recover the sensible heat of the crude gas by the exchange of heat between the crude gas and tar. However, crude gas generated in a coke oven contains naphthalene and other soluble substances as well as dust and these materials mix and accumulate in the high boiling point oil, such as tar, and the mixture blocks the high boiling point oil spray nozzle used in such spraying systems. This clogs the circulating system and serves to decompose and deteriorate the high boiling point oil, which makes it difficult to operate such a system for any reasonable length of time under stable conditions.